Routine mammogram screening for women in their 40s does not significantly reduce deaths from breast cancer, a review suggests.
Giving women annual mammograms starting at age 40 would save about four lives for every 1,000 women screened, but the benefits need to be weighed against the risks of radiation from the tests, the anxiety of false positive results and higher costs, the researchers say in Saturday's issue of The Lancet.
"Each woman needs to have a very personal discussion with her doctor about the potential risks and benefits of undergoing mammography before they reach 50," said Dr. Gary Lyman, a breast oncologist at the University of Rochester who co-authored a commentary on the study.
"Clearly, if a young woman’s risk of breast cancer is at all increased due to family history and other factors, the benefit will almost always outweigh any risk."
In Canada, screening for breast cancer is recommended every one to two years for women aged 50 and older.
Lyman and his co-authors reviewed 10 clinical trials to see if routine mammography increased survival for women aged 40 to 50.
In the study, more than 160,000 women in Britain were randomly assigned to have annual mammograms starting at age 40 or age 50. Participants were tracked for an average of 11 years.
Breast cancer deaths dropped by 17 per cent in the younger screening group, but the difference was not statistically significant, the researchers said.
Among women who had regular mammograms from age 40, 23 per cent had at least one false positive result, where the test points to breast cancer that later turns out not to be the case, compared with about 12 per cent in the older group.
"Although the best estimates of harms from screening mammography seem to be less than the benefits, they remain too uncertain to conclude that screening mammography in this age group is associated with a net benefit," Benjamin Djulbegovic of the H. Lee Moffitt Cancer Center and Research Institute in Tampa, Fla., wrote in an accompanying comment.
Women of all ages, particular older women in whom breast cancer is more common, are urged to see their doctor immediately if they notice any changes in their breasts, said Prof. John Toy of the charity Cancer Research UK, which funded the study.
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